1. Field of the Invention
The invention is related to methods and apparatus for use in drilling and completion operations on a subsea well from an offshore drilling rig, particularly in those operations which involve running and retrieving the subsea-deployed blowout preventer (BOP) stack.
2. Description of Related Art
Historically, a subsea-deployed blowout preventer (BOP) stack performs most of its drilling functions with a downwardly opening funnel located at the bottom of the stack at the BOP-mounted wellhead connector. The funnel allows the operator to capture the wellhead while the BOP stack is suspended over location from the drilling rig. However, when the operator switches from drilling to completion operations, the BOP stack must usually enter (stab into) subsea equipment that has a funnel-up configuration. This means that the downwardly opening facing funnel on the BOP stack must be removed in order for the BOP to stab into the subsea equipment. Prior to the present invention, in order to remove the funnel, the BOP had to be xe2x80x9ctrippedxe2x80x9d to the surface, a routine but costly and time-consuming operation. However, in deepwater applications in recent years, this has begun to be an extremely costly trip (taking upwards of 2-3 days and more at rig rates of greater than $200,000/day). Furthermore, when completion operations are over and it is time to switch the BOP stack configuration back to a drilling mode, the funnel must be re-installed on the BOP stack in order to enable the BOP stack to capture the next wellhead. This requires still another xe2x80x9ctrippingxe2x80x9d operation to bring the BOP back to the surface and into the BOP storage area on the drilling rig in order to reinstall the funnel. The re-installation at the surface involves substantial manpower and heavy lifting equipment and is considered a dangerous activity due to the weight of the funnel (5-6,000 lbs.) and its location at the bottom of the BOP stack. It is the purpose of the present invention, therefore, to eliminate the costly, time-consuming and dangerous xe2x80x9ctrippingxe2x80x9d operational requirements of the prior art.
The invention is a device whose purpose is to eliminate the xe2x80x9ctrippingxe2x80x9d of the BOP stack when it is desired to switch operations between drilling and completion activities. The device is a new mechanism for attaching a BOP guide funnel and which will allow the guide funnel to be released and/or reattached while the BOP remains subsea on or near the seafloor. The new BOP funnel mechanism consists of three basic components: a guide funnel, a connector shroud and a parking pile adapter. The guide funnel is a structure with a downwardly opening funnel on the bottom (used to capture a wellhead) and an upwardly opening smaller funnel on top (used to guide the shroud back into the guide funnel during re-installation of the funnel). The connector shroud is a structure that is permanently attached to the bottom of the BOP stack. It surrounds the BOP wellhead connector and holds the guide funnel in place. The connector shroud also acts as a guide allowing the BOP stack to enter other subsea equipment, which is designed in a funnel-up configuration. The connector shroud includes a latching mechanism for releasing and/or reattaching the guide wide funnel. The latching mechanism may be controlled either by the BOP control system or by intervention from a remotely operated vehicle (ROV). The parking pile adapter is a structure designed to xe2x80x9cstorexe2x80x9d the funnel at the seafloor after it has been released from the BOP stack.